The present application has some FIGS. in common with, but is not necessarily otherwise related to, the following application(s), which are commonly owned with and have the same effective filing as the present application, and which are all hereby incorporated by reference:
application Ser. No. 10/040,301 filed Oct. 26, 2001 (Atty. Docket SC-00-10);
application Ser. No. 10/040,927 filed Oct. 26, 2001 (Atty. Docket SC-00-11);
application Ser. No. 10/035,350 filed Oct. 26, 2001 (Atty. Docket SC-00-12);
application Ser. No. 10/040,294 filed Oct. 26, 2001 (Atty. Docket SC-01-03);
application Ser. No. 10/040,928 filed Oct. 26, 2001 (Atty. Docket SC-01-04); and
application Ser. No. 10/036,105 filed Oct. 26, 2001 (Atty. Docket SC-01-05).
The present invention relates to systems, methods, and subassemblies for drilling oil, gas, and analogous wells, and more particularly to downhole failure detection.
Background: Downhole Bit Failure
When drilling a well it is desirable to drill as long as possible without wearing the bit to the point of catastrophic bit failure. Optimum bit use occurs when a bit is worn sufficiently that the useful life of the bit has been expended, but the wear is not so extensive that there is a high likelihood of mechanical failure which might result in leaving a portion of the bit in the well. Poor drilling performance, increased BHA (Bottom Hole Assembly) wear, and more frequent fishing jobs all result from continued drilling with bits which are in the process of mechanical failure. A system capable of detecting the early stages of bit failure, with the additional capability of warning the operator at the surface, would be of great value solving the problem of drilling to the point of catastrophic bit failure.
The innovations in this application provide a reliable, inexpensive means of early detection and operator warning when there is a roller cone drill bit failure. This system is technically and economically suitable for use in low cost rotary land rig drilling operations as well as high-end offshore drilling. The solution is able to detect impending bit failure prior to catastrophic damage to the bit, but well after the majority of the bit life is expended. In addition to failure detection, the innovative system is able to alert the operator at the surface once an impending bit failure is detected.
The problem of downhole bit failure can be broken down into two parts. The first part of the problem is to develop a failure detection method and the second part of the problem is to develop a method to warn the operator at the surface. Several approaches for detecting bit failure have been considered.
It appears that some work has been done on placing sensors directly in the drill bit assembly to monitor the bit condition. There is some merit in placing sensors in the bit assembly, but this methodology also has some distinct disadvantages. The main disadvantage is the necessity of redesigning every bit which will use the method. In addition to being costly, each new bit design will have to accommodate the embedded sensors which might compromise the overall design. A second disadvantage arises from the fact that sensor connections and/or data transmission must be made across the threaded connection on the bit to a data processing or telemetry unit. This is difficult in practice.
Downhole Power
In any system that uses electronic components there must be a power source. In many downhole tools disposable batteries are used to power electronics. Batteries have the desirable characteristics of high power density and ease of use. Batteries that are suitable for high-temperature, downhole use have the undesirable characteristics of high cost and difficulty of disposal. Batteries are often the only solution for powering downhole tools requiring relatively high power levels.
Differential Sensor Measurement Method and Apparatus to Detect a Drill Bit Failure and Signal Surface Operator
This application discloses a system and method for detecting downhole drill bit failure and signalling that failure to an operator. In one example embodiment, downhole sensors located in a sub assembly (or in the bit itself) are monitored, and cross comparisons between sensors are performed. Sensors might include temperature, acceleration, or any other type of sensor that will be affected by a bit failure. In the preferred embodiment, an absolute sensor reading from any one sensor is not used to determine bit failure. Instead, a measurement of one sensor relative to the other sensors is used.
The changes in sensor readings which do indicate failure are reported to the operator. For example, the signal may be sent as variation in the downhole pressure. The pressure is controlled with a bypass port located above the bit. Opening the port decreases pressure, closing the port restores it. Such changes in pressure are easily detected by the operator.
The disclosed innovations, in various embodiments, provide one or more of at least the following advantages:
self calibrating: requires no pre-drilling data gathering with sensors to calibrate;
robust detection of change in operations at the time of failure, even if the physics are not well understood;
no special bit required;
design-independent prediction of bit failure;
adaptable to varying drilling conditions;
early detection of bit failure reduces fishing; and
early detection of bit failure permits greatly improved failure analysis (since bits can be pulled in time for informative routine analysis, without significant loss of running time) and hence rapid improvements in bit design.